1. Technical Field
The present invention relates to a double-bag package constructed using a modified vertical form and fill packaging machine and a modified perforation knife, and the method for making same, that provides for a single piece construction of a package having two horizontally adjacent bags joined together by a perforated vertical seal having self-correcting directional perforations. The package is suitable for retail snack food distribution. The invention allows for use of existing film converter and packaging technology to produce a double-bag package with minimal increased costs and minimal modification.
2. Description of Related Art
Vertical Form, Fill and Seal Machines
Vertical form, fill and seal packaging machines are commonly used in the snack food industry for forming, filling and sealing bags of chips and other like products. Such packaging machines take a packaging film from a sheet roll and form the film into a vertical tube around a product delivery cylinder. The vertical tube is vertically sealed along its length to form a back seal. The machine applies a pair of heat-sealing jaws or facings against the tube to form a transverse seal. This transverse seal acts as the top seal on the bag below and the bottom seal on the package being filled and formed above. The product to be packaged, such as potato chips, is dropped through the product delivery cylinder, into the formed tube, and is held within the tube above the bottom transverse seal. After the package has been filled, the film tube is pushed downward to draw out another package length. A transverse seal is formed above the product, thus sealing it within the film tube and forming a package of product. The package below said transverse seal is separated from the rest of the film tube by cutting across the sealed area.
One such packaging machine is seen diagrammatically in FIG. 9. This drawing is simplified, and does not show the cabinet and support structures that typically surround such a machine, but it demonstrates the working of the machine well. Packaging film 910 is taken from a roll 912 of film and passed through tensioners 914 that keep it taut. The film then passes over a former 916, which directs the film into a vertical tube around a product delivery cylinder 918. As the tube is pulled downward by drive belts 920, the vertical tube of film is sealed along its length by a vertical sealer 922, forming a back seal 924. The machine then applies a pair of heat-sealing jaws 926 against the tube to form a transverse seal 928. This transverse seal 928 acts as the top seal on the bag 930 below the sealing jaws 926 and the bottom seal on the bag 932 being filled and formed above the jaws 926. After the transverse seal 928 has been formed, a cut is made across the sealed area to separate the finished bag 930 below the seal 928 from the partially completed bag 932 above the seal. The film tube is then pushed downward to draw out another package length. Before the sealing jaws form each transverse seal, the product to be packaged is dropped through the product delivery cylinder 918 and is held within the tube above the transverse seal 928.
The material that is fed into the form, fill and seal machine is typically a packaging film, such as polypropylene, polyester, paper, polyolefin extrusions, adhesive laminates, and other such materials, or from layered combinations of the above. For many food products, where flavor retention is important, a metalized layer will form the innermost layer.
The form, fill and seal machines are quite expensive, in the range of $250,000 each, but pay for themselves easily when compared to the cost of pre-formed bags and the machinery to fill them. However, in order to maximize the productivity of the form, fill and seal machines, it is common for the product delivery tube 918 and former 916 to be made as a unit that is easily interchangeable in less than 15 minutes. The length of the transverse seal can also be changed, by exchanging the sealing jaws, or in some cases, merely by exchanging the facing (the portion of the sealing jaws which actually makes contact with the packaging film). By changing these elements, as well as the width of film roll feeding into the machine and the programming of the machine, one form, fill and seal machine can handle a number of different products in different size packages, limited primarily by the width of film the machine will handle, the maximum length of bag the machine is designed to handle, and the available former/delivery tube assemblies.
Packaging Film
The packaging film used in such process is typically a composite polymer material produced by a film converter. For example, one prior art composite film used for packaging potato chips and like products is illustrated in FIG. 1, which is a schematic of a cross-section of the film illustrating each individual substantive layer. FIG. 1 shows a sealable inside, or product side, layer 16 which typically comprises metalized oriented polypropylene (“OPP”) or metalized polyethylene terephtalate (“PET”). This is followed by a laminate layer 14, typically a polyethylene extrusion, and an ink or graphics layer 12. The ink layer 12 is typically used for the presentation of graphics that can be viewed through a transparent outside layer 10, which layer 10 is typically OPP or PET.
The prior art film composition shown in FIG. 1 is ideally suited for use on vertical form and fill machines for the packaging of food products. The metalized inside layer 16, which is usually metalized with a thin layer of aluminum, provides excellent barrier properties. The use of OPP or PET for the outside layer 10 and the inside layer 16 further makes it possible to heat seal any surface of the film to any other surface in forming either the transverse seals or back seal of a package.
Typical back seals formed using the film composition shown in FIG. 1 are illustrated in FIGS. 2a and 2b. FIG. 2a is a schematic of a “lap seal” embodiment of a back seal being formed on a tube of film. FIG. 2b illustrates a “fin seal” embodiment of a back seal being formed on a tube of film.
With reference to FIG. 2a, a portion of the inside metalized layer 26 is mated with a portion of the outside layer 20 in the area indicated by the arrows to form a lap seal. The seal in this area is accomplished by applying heat and pressure to the film in such area. The lap seal design shown in FIG. 2a insures that the product to be placed inside the formed package will be protected from the ink layer by the metalized inside layer 26.
The fin seal variation shown in FIG. 2b also provides that the product to be placed in the formed package will be protected from the ink layer by the metalized inside layer 26. Again, the outside layer 20 does not contact any product. In the embodiment shown in FIG. 2b, however, the inside layer 26 is folded over and then sealed on itself in the area indicated by the arrows. Again, this seal is accomplished by the application of heat and pressure to the film in the area illustrated.
Packaging
Regardless of whether a lap seal or fin seal is used for constructing a standard package using a vertical form and fill packaging machine, the end result is a package as shown in FIG. 3a with horizontally oriented top and bottom transverse seals 31, 33. Such package is referred to in the art as a “vertical flex bag” or “pillow pouch,” and is commonly used for packaging snack foods such as potato chips, tortilla chips, and other various sheeted and extruded products. The back seal discussed with reference to FIGS. 2a and 2b runs vertically along the bag and is typically centered on the back of the package shown in FIG. 3a, thus not visible in FIG. 3a. Because of the narrow, single edge base on the package shown in FIG. 3a formed by the bottom transverse seal 33, such prior art packages are not particularly stable when standing on one end. This shortcoming has been addressed in the packaging industry by the development of a horizontal stand-up pouch such as the embodiment illustrated in FIGS. 4a, 4b, and 4c. As can be seen by reference to said figures, such horizontal stand-up pouch has a relatively broad and flat base 47 having two contact edges. This allows for the pouch to rest on this base 47 in a vertical presentation. Manufacture of such horizontal stand-up pouches, however, does not involve the use of standard vertical form, fill, and seal machines but, rather, involves an expensive and relatively slow 3-piece construction using a pouch form, fill, and seal machine.
Referring to FIGS. 4b and 4c, the horizontal stand-up pouch of the prior art is constructed of three separate pieces of film that are mated together, namely, a front sheet 41, a rear sheet 43, and a base sheet 45. The front sheet 41 and rear sheet 43 are sealed against each other around their edges, typically by heat sealing. The base sheet 45 is, however, first secured along its outer edges to the outer edges of the bottom of the front sheet 41 and rear sheet 43, as is best illustrated in FIG. 4c. Likewise, the mating of the base sheet 45 to the front sheet 41 and the rear sheet 43 is also accomplished typically by a heat seal. The requirement that such horizontal stand-up pouch be constructed of three pieces results in a package that is significantly more expensive to construct than a standard form and fill vertical flex bag.
Further disadvantages of using horizontal stand-up pouches include the initial capital expense of the horizontal stand-up pouch machines, the additional gas flush volume required during packaging as compared to a vertical flex bag, increased down time to change the bag size, slower bag forming speed, and a decreased bag size range. For example, a Polaris model vertical form, fill, and seal machine manufactured by Klick Lock Woodman of Georgia, USA, with a volume capacity of 60-100 bags per minute costs in the range of $75,000.00 per machine. A typical horizontal stand-up pouch manufacturing machine manufactured by Roberts Packaging of Battle Creek, Mich., with a bag capacity of 40-60 bags per minute typically costs $500,000.00. The film cost for a standard vertical form, fill, and seal package is approximately $0.04 per bag with a comparable horizontal stand-up pouch costing roughly twice as much. Horizontal stand-up pouches further require more than twice the oxygen or nitrogen gas flush. Changing the bag size on a horizontal stand-up pouch further takes in excess of two hours, typically, while a vertical form and fill machine bag size can be changed in a matter of minutes. Also, the typical bag size range on a horizontal stand-up pouch machine is from 4 oz. to 10 oz., while a vertical form and fill machine can typically make bags in the size range of 1 oz. to 24 oz.
One advantage of a horizontal stand-up pouch machine over a vertical form and fill machine, however, is the relatively simple additional step of adding a zipper seal at the top of the bag for reclosing of the bag. Vertical form and fill machines typically require substantial modification and/or the use of zipper seals premounted on the film oriented horizontally to the seal facings used to seal the horizontal transverse seals.
An alternative approach taken in the prior art to producing a bag with more of a stand-up presentation is the construction of a flat bottom bag such as illustrated in FIG. 3b. Such bag is constructed in a method very similar to that described above with regard to prior art pillow pouches. However, in order to form the vertical gussets 37 on either side of the bag, the vertical form, fill, and seal machine must be substantially modified by the addition of two movable devices on opposite sides of the sealing carriage that move in and out to make contact with the packaging film tube in order to form the tuck that becomes the gussets 37 shown in FIG. 3b. Specifically, when a tube is pushed down to form the next bag, two triangular shaped devices are moved horizontally towards the packaging film tube until two vertical tucks are formed on the packaging film tube above the transverse seals by virtue of contact with these moving triangular shaped devices. While the two triangular shaped devices are thus in contact with the packaging tube, the bottom transverse seal is formed. The package is constructed with an outer layer 30 that is non-sealable, such as paper. This causes the formation of a V-shaped gusset 37 along each vertical edge of the package when the transverse seals 31, 33 are formed. While the triangular shaped devices are still in contact with the tube of packaging material, the product is dropped through the forming tube into the tube of packaging film that is sealed at one end by virtue of the lower transverse seal 33. The triangular shaped devices are then removed from contact with the tube of packaging film and the film is pushed down for the formation of the next package. The process is repeated such that the lower transverse seal 33 of the package above and upper transverse seal 31 of the package below are then formed. This transverse seal is then cut, thereby releasing a formed and filled package from the machine having the distinctive vertical gussets 37 shown in FIG. 3b. 
The prior art method described above forms a package with a relatively broad base due to the V-shaped vertical gussets 37. Consequently, it is commonly referred to in the art as a flat bottom bag. Such flat bottom bag is advantageous over the previously described horizontal stand-up pouch in that it is formed on a vertical form, fill, and seal machine, albeit with major modifications. However, the prior art method of making a flat bottom bag has a number of significant drawbacks. For example, the capital expense for modifying the vertical form, fill, and seal machine to include the moving triangular-shaped devices is approximately $30,000.00 per machine. The changeover time to convert a vertical form, fill, and seal machine from a standard pillow pouch configuration to a stand-up bag configuration can be substantial, and generally in the neighborhood of one-quarter man hours. The addition of all of the moving parts required for the triangular-shaped devices to move in and out of position during each package formation cycle also adds complexity to the vertical form, fill, and seal machine, inevitably resulting in maintenance issues. Importantly, the vertical form, fill, and seal machine modified to include the moving triangular-shaped devices is significantly slower than a vertical form, fill, and seal machine without such devices because of these moving components that form the vertical gussets. For example, in the formation of a six inch by nine inch bag, the maximum run speed for a modified vertical form, fill, and seal machine using the triangular-shaped moving devices is in the range of 15 to 20 bags per minute. A standard vertical form, fill, and seal machine without such modification can construct a similarly sized pillow pouch at the rate of approximately 40 bags per minute.
Multipacks
A popular marketing concept is that of packaging two or more individually sealed items together. While the marketing idea of multi-packs may be simple, the translation of that idea to current packaging technology can be more difficult. Often, rather than packaging a product into several different packages at the same time, each package is separately produced, as usual, then the various packages are boxed together or over-wrapped to form a multi-pack. It would be preferable to be able to produce multiple packages fastened together for sales, but which could be separated by the consumer for convenience.
One example of a prior art multi-pack package is disclosed in U.S. patent application Ser. No. 10/100,360, Publication No. US 2003/0009989. FIG. 5a is a perspective view of a multi-pack package 500 in accordance with the '360 application. FIG. 5b is a top-down cross-sectional view of the multi-pack package 500 shown in FIG. 5a. The multi-pack package 500 has two side-by-side bags 510a, 510b attached together by a vertical seal 506 having perforations 508. The package also has top and bottom horizontal/transverse seals 502, 504, as well as vertical gussets on the left and right sides of the package. The double-bag package of the '360 application provides consumers with two containers conveniently fastened together. However, there are several disadvantages to the '360 application's multi-pack package and method for making the package.
One disadvantage is that the package 500 requires a special, complex vertical form, fill and seal (VFFS) machine having two feed tubes. FIG. 6a is a front view of the former/delivery tube assembly of such of a twin-feed VFFS machine, and FIG. 6b is a side view of the former/delivery tube assembly shown in FIG. 6a. FIG. 7 is a cross-section of the former/delivery tube assembly taken at point 7-7′ of FIG. 6b, and FIG. 8 is a cross-section of the former/delivery tube assembly taken at point 8-8′ of FIG. 6b. A twin-feed VFFS having a special former/delivery tube assembly such as that depicted in FIG. 6a has a greater initial capital cost than a traditional VFFS machine. Furthermore, such a modified twin-feed VFFS machine requires a substantially wider film stock than traditional VFFS machines. The use of non-standard film stock and former/delivery tube assemblies undesirably increases the capital and operating costs. Additionally, no equipment currently exists to make seals wider than 18 inches, severely limiting bag sizes.
Another disadvantage is that each container of the multi-pack package disclosed in the '360 application has more restrictive extremities than does a pillow pouch (or vertical flex bag), such as that shown in FIG. 3a, formed from a traditional VFFS machine. Whereas a traditional pillow pouch bag has flat seals on only two opposing sides, each container of the multi-pack package shown in the '360 application, which is depicted in FIG. 5a, has flat seals on every side but one. Each flat seal flattens the package in the surrounding area, thus decreasing the available volume within the package. Because the multi-pack package disclosed in the '360 application has more flat seals per container than traditional pillow pouches, the multi-pack package disclosed therein has less available volume for product than traditional pillow pouches.
FIG. 5c is a perspective view of a prior art saddle-bag package, which is another example of a multi-pack package. The saddle-bag package 550 comprises two pouch-type bags 552, 554 that share a top transverse seal 558. The saddle-bag package 550 is typically oriented so that the back sides of each of the connected pouches 552, 554 face each other. The package 550 then stands on the bottom transverse seals 556, 560 of each pouch 552, 554. The graphics and/or text on both pouches 552, 554 of the saddle-bag package 550 typically appear upright when the package 550 is so positioned. When forming saddle-bag packages using a vertical form, fill and seal machine, the film feed typically has graphics/text units that alternate between upside-down and right-side up and are linked together vertically (as a column of graphical/text units as opposed to a row of graphical/text units). Printing graphics and/or text units in such an alternating fashion can require modifications to the printing process and thus undesirably increase costs.
Perforations and Perforating Knife
It is well known in the art that films or sheets can be perforated to make such films or sheets easily separated into two or more pieces. Perforations allow films or sheets of material to be more controllably torn along a perforation path. FIG. 12 is an elevated top view of a common prior art perforation pattern comprising a series of oval-shaped perforations 1220 that are spaced along a perforation path 1210 in a film 1202. Such oval-shaped perforations 1220 are often formed using an anvil and a rotating perforating wheel having oval-shaped blades or punchers. FIG. 13 is an elevated top view of another common prior art perforation pattern comprising a series of I-shaped perforations 1330 that are spaced along a perforation path 1310 in a film 1302. Such I-shaped perforations 1330 can be formed using an anvil and a rotating perforating wheel having I-shaped blades or punchers, or they can be formed using a perforating blade having teeth that form I-shaped incisions.
While films having little or no orientation, such as low-density polyethylene (LDPE), are generally more resistant to tearing than oriented films, once a tear is initiated in films having low orientation, it will generally propagate in the direction of the tearing force. Thus, a tear initiated along a perforation path in a low-orientation film tends to propagate predictably from one perforation to the next. In contrast, while oriented films such as biaxially oriented polypropylene (BOPP) generally have a lower tearing resistance than films having low orientation, once a tear is initiated, it will not necessarily propagate in the direction of the tearing force. This is because the tears have a tendency to propagate along the direction (or directions) of orientation/stretching. Oriented films are thus more likely to suffer from errant or stray tears than non-oriented films.
Many prior art perforation knife designs do not produce perforations that are adequate for reliable separation of oriented-film flexible packages along the desired perforation paths. The perforations created by such prior art knife designs require that the tears between perforations propagate in a straight line for separation to be successful. For example, if the film 1202 with prior art oval perforations 1220 shown in FIG. 12 comprises BOPP, errant tears 1230 will likely miss the next perforation along the perforation path 1210. Likewise, if the film 1302 with prior art I-shaped perforations 1320 shown in FIG. 13 comprises BOPP, an errant tear 1330 propagating from the end of an I-shaped perforation will likely miss the next I-shaped perforation 1320 along the perforation path 1310. While the use of certain expensive films, such as polyester (PET), can improve the predictability of tearing, it still does not provide a fail-safe solution. Thus, it would be desirable to have a perforation pattern capable of capturing and redirecting errant tears for fail-safe separation. It would be desirable to have a perforation knife for creating such perforation patterns. Furthermore, it would be desirable to have a low-cost oriented packaging film with more predictable tearing properties.
Consequently, a need exists for a method for forming a multi-pack package using standard vertical form, fill, and seal machine technology and a single sheet of packaging film. This method should ideally produce a double-bag package having two horizontally adjacent bags detachably connected by a perforated seal. Such method should produce such a package using a single vertical form, fill, and seal machine and a modified perforation knife. The modified perforation knife should create perforation patterns capable of capturing and redirecting errant tears for fail-safe separation along a desired perforation path.